1. Field of the Invention
The present invention relates to a device for moving a winding shaft in a shutter used for a building. In particular, the winding shaft can be automatically moved in accordance with the winding diameter, which varies depending on the winding and unwinding of the shutter curtain.
2. Description of the Related Art
In general, the winding diameter of a winding shaft varies according to the winding and unwinding of the shutter curtain. Conventionally, since the winding shaft is attached to a case adjacent to the support, such as the building, the movement of pulling out the shutter curtain from the winding shaft to the shutter guide shifts as the winding diameter varies. In particular, when the shutter curtain approaches the closed state, in which the winding diameter becomes smaller, the shutter curtain abuts against the shutter guide. This impact produces a loud noise, damages the slats, peels off the paint, and accelerates the wear of sound-deadening members, for example. Accordingly, the shutter curtain becomes rusty, and its life is shortened.
To overcome the above drawbacks, the applicant of the present invention has disclosed a shutter in which the winding shaft moves in accordance with the winding diameter in Japanese Patent Application No. 63-124423 (Japanese Utility Model Laid-Open No. 2-45293.) Such a shutter is simply constructed with a bearing plate that pivots the winding shaft and is supported by a pair of links. With such a simple construction, according to the change of the winding diameter, a quick response can be made to move the winding shaft reliably. Thereby, the problems inherent in a conventional shaft secured to the support are solved. However, such a shutter is constructed with the pair of links 68 extending upward through the outer circumference of the winding wheel, as shown in FIG. 8. Thus, a space for arranging the links 68a and 68b must be ensured between the right and left ends of the winding wheel 4 and a side wall 2b secured to the support for swingably supporting the links 68. Thus, the dimension of the space accommodating the links 68 must be enlarged. This prevents the shutter case from being downsized, and therefore the resulting shutter case is not suitable in limited spaces.